The wikipedia entry for cold iron references Kipling and Walter Scott. Wondering if there are any surviving folktales involving iron as a ward or weapon against faeries and other supernatural entities.
European folklore is replete with mentions of supernatural creatures being averse to iron, especially in the northwestern and northeastern regions. (Allow me also to highlight for passersby, as mentioned in the article you linked, that “cold iron” traditionally just signifies normal, plain-ol' iron, but nowadays the meaning is often extended to more fanciful connotations.)
The article you mentioned already discusses horseshoes, which were common apotropaic items. There were also many things iron served well as a practical construction material for, like gates and bedframes, to which it would lend the added peace of mind of deterring evil.
Insofar as folklore, here are some common motifs to get your research started:
A faerie marries a mortal man, either a) on the specific condition she not touch iron, or b) that her husband not strike her, which he eventually inadvertently does with something that just happens to be made of iron. The Welsh Llyn y Fan Fach tale with it’s many variants are the archetypal example of this theme.
More generalized than the article you linked (which mentions burying a knife specifically), in many tales simply burying anything iron beneath the threshold of your home or property will keep out both malicious or helpful creatures. In other tales the item need only be hung on the outside of the house (like horseshoes).
Tales in which a friendly faerie needs help repairing something made of iron, or borrowing something made of iron (often a cooking utensil). In these instances, it seems there is something about the faerie owning the item or some constraint upon how they can handle it which is the problem, as the faeries are still able to touch the iron safely in the tales.